The first commercially attractive cellular telephones or terminals were introduced in the market at the end of the 1980's. Since then, a lot of effort has been made in making smaller terminals, with much help from the miniaturisation of electronic components and the development of more efficient batteries. Today, numerous manufacturers offer pocket-sized terminals with a wide variety of capabilities and services, such as packet-oriented transmission and multiple radio band coverage. In order to attract customers the terminal manufacturers have therefore taken further measures to strengthen their position in the competition, one such being to offer terminals with detachable covers or covers. If a user wishes to change the outer appearance of his communication terminal, he can simply buy a new cover of the desired kind. The old cover is preferably released by a simple grip without the aid of tools, where after the new cover can be snapped on. A detachable cover is generally a fairly simple element, essentially formed from a single piece of plastic or possibly metal. The cover may represent only the front side of the terminal, i.e. the side of the terminal carrying the user interface generally comprising a terminal display and keypad, a microphone and a loudspeaker. In such a design, the cover forms a separate part of the cover of the terminal, or optionally an auxiliary part to be attached outside the cover. Alternatively, the cover may include more than one piece, e.g. a front piece and a back piece devised to substantially enclose the terminal. The detachable covers are often provided in different colours, and also with more advanced patterns such as logos or images. The detachable covers of the prior art mainly create an aesthetic effect, changing the visual appearance of the terminal, but may also comprise means for affecting the functions of the terminal.
A housing, detachable or not, devised to cover a terminal front side, or part thereof, is generally arranged with a transparent front window which allows the display to be seen there through and at the same time protects the display. In order to prevent moisture or dust to enter the space between the display and the protective window, a sealing gasket is generally arranged there between. The gasket is often devised to engage a portion of a plastic carrier frame surrounding the display. A problem with such an arrangement is that the surface of the plastic carrier, facing the protective window, is generally neither sufficiently flat nor wide enough to guarantee a secure seal. If the surface of the plastic carrier is widened, the size of the display module will increase, which counteracts the general desire to provide as small terminals as possible.
An alternative state of the art solution is shown in FIG. 1, illustrating a cross-sectional view of a part of a display module 1, with a front side facing upwards. Therein it is clearly illustrated that a display 2 is supported by the plastic carrier 3. In the illustrated prior art embodiment, the display 2 is a Liquid Crystal Display LCD, comprising two glasses with an intermediate layer of liquid crystals. On top of the outermost glass, a polariser 5 is attached. A dust gasket 6 is provided over the edge of polariser 5, devised to engage with a housing of an electronic device into which the display module is to be mounted. A problem with this prior art solution is that when the gasket 6 is applied as illustrated, it may wrinkle causing poor sealing. Moving the gasket further towards the centre of the display module 1 to a flat surface portion of polariser 5, i.e. to the right in the drawing, will decrease the visible part of the display and therefore have a negative effect on the display dimension.
Another problem related to display modules concerns its connection to other parts of an electronic device, such as to a printed circuit board, PCB. FIG. 2 illustrates a cross-sectional view of a part of a prior art display module 1 with an LCD 2 and a polariser 5. A driver 12 is connected to the LCD 2, for applying voltages to the crystals of the LCD 2. A flexible printed circuit board FPC 13 acts as a bus to base band circuits of an electronic device carrying the display module 1. The FPC 13 is sensitive, and optionally also carries some components 14. A plastic carrier for the LCD 2 is preferably included in the display module 1 as well, as in the solution of FIG. 1, but is left out in this drawing for the sake of clarity. Said plastic carrier may also have a cut-out or recessed portioned at the place where the FPC is arranged, such that the FPC does not need to extend around the plastic carrier. Many electronic devices of today, particularly mobile phones, have replaceable covers or housings 11. However, since the FPC 13 is sensitive it may be damaged when the housing 11 is off, or during assembly. Furthermore, the curvature of the FPC allocates some space that could be used for other purposes, or for making the electronic device smaller.
Yet another problem associated with display modules is related to their sensitivity to electrostatic discharge, ESD. However, there is little room outside the LCD to provide an ESD connection to the electronic device, when small dimensions are desired. Furthermore, the ESD connection should preferably be placed close to a battery connector of the electronic device, such as a radio communication terminal.